Friction materials have been widely used in drive technology, in particular in clutches, gears or brakes. The friction coefficient of the friction materials is intended to be as high and constant as possible.
Production of friction linings based on sintered friction materials is cost-effective. In particular foil technology and scatter-sintering processes are used. In foil technology, suitable powder blends are pre-pressed by pressing tools into thin rings which are then sintered onto an optionally pre-treated carrier material by pressure sintering. In the scatter-sintering process, the friction material is scattered onto a carrier in the form of a powder blend and then passed through a sintering furnace. Binding of the sintered friction material to the carrier can be improved by an adhesion promoter that can optionally be scattered onto the carrier as a thin layer. Friction rings having a friction lining produced by means of the scatter-sintering process are, for example, described in DE 36 09 879.
EP 0 505 345 B2 discloses a sintered friction material for friction linings of clutches and brakes containing powdery and/or granular metallic and non-metallic constituents, at least one of the metallic constituents predominantly or completely consisting of brass. In particular, the friction material can be composed of brass, quartzite, graphite, aluminum oxide, tin, and iron.
From DE 197 11 830 C2 a sintered brake lining for a braking element made of fiber-reinforced ceramic is known, containing primary carbon and metallic particles that are at least partially reaction-bonded to the primary or pyrolytically formed carbon. In addition, the brake lining can include additives of hard material particles, pyrolyzed organic binders or solid lubricants.
DE 103 38 200 B4 describes clutch linings made of fiber-reinforced ceramic materials containing fibers made of carbon, and whose matrix material is selected from inorganic polymers, oxidic ceramics, set cements, element-organic polymers, and inorganic disperse solids held together by an inorganic or organic binder. In addition, the matrix material can contain inorganic disperse solids selected from silicon dioxide, silicon nitride, aluminum oxide, titanium dioxide, titanium carbide, tungsten carbide, silicates, and titanates, and be bound by inorganic compounds forming glass phases.
DE 2012147 A1 shows a safety brake mechanism for rail-mounted means of conveyance in mining having at least one brake shoe that can be pressed to a guide rail whose brake surface is provided with a friction-increasing coating. The coating comprises a solder layer in which coarse carbide particles of a grain size of approximately 1.5 to 3 mm are embedded at a short distance from each other.
EP 1 666 75 discloses a friction apparatus having at least one pair of sliding surfaces brought into contact with each other. The friction apparatus comprises a friction surface containing silicon carbide and a friction surface counterpart with a cermet layer containing tungsten carbide. The cermet layer can be applied onto a carrier by flame spraying.
Although friction linings made of sintered friction materials can be produced cost-effectively, as compared to carbon-based friction linings, they have a lower friction coefficient level. In addition, friction behavior in sintered friction materials for oil operation strongly depends on the gear oil used.